This patch changes the location querying code so that:
1. We're populating structures corresponding to SCIP instead of LSIF
(with "scheme" and "identifier" inside "MonikerData")
2. Avoid repeatedly allocating a constant string 'scip' for the scheme
only to throw it away later.
3. Makes the two queries and their scanning code more similar for easier
comparison. When I land precise usagesForSymbol, I will de-duplicate
some of the scanning code between these two queries.
I have avoided renaming all of the local variables to avoid creating
more noise.
## Test plan
Covered by existing tests.
